DNS settings for Webmin/Virtualmin with multiple domains

I have three domains, lets call them maindomain.com, domain1.com and domain2.com I have a VPS with ip 111.222.333.444 and i've set the hostname to node.maindomain.com I want to use maindomain.com as the main one where I install virtualmin/webmin.

At my domain registrar, I have these DNS settings (my registrar requires you create a DNS zone if you use their nameservers:

I have their nameservers main.nameserver1.com and main.nameserver2.com and in the DNS zone for maindomain.com I have the following:

@ A 14400 111.222.333.444
admin A 14440 111.222.333.444
mail CNAME 14400 maindomain.com
www CNAME 14400 maindomain.com
ftp CNAME 14400 maindomain.com
node CNAME 14400 maindomain.com
webmail CNAME 14440 maindomain.com
@ MX 14400 0 maindomain.com

I want to add domain1.com and domain2.com to this server. And then I want to be able to setup email accounts on domain1.com and domain2.com. I would prefer that the IMAP server settings for Thunderbird, Outlook etc for domain1.com and domain2.com be mail.domain1.com and mail.domain2.com. I also need SSL on all domains. I tried using the autoinstaller and then adding domain1.com as a virtual server and it works. However I can only receive email and not send email, I get a SMTP authentication error.

I am willing to start from scratch as I have no content on any of the sites. I am very confused about the DNS stuff. Can someone please help me with getting this right? I have been at it for a couple of weeks and I don't know where and what I should put for the DNS records for domain1.com and domain2.com.

Basically, I set the hostname on my vps to node.maindomain.com and ran the autoinstaller. I don't necessarily need the node. subdomain but someone said something about reverse DNS for email etc. What is the simplest way to get this up and running without messing around too much with config files or DNS? I would really really appreciate a workflow when it comes to setting things up after the autoinstaller, adding a new domain and then setting the relevant DNS records.